Flaxseed meal (FM) is rich in the plant lignan secoisolariciresinol diglucoside (SDG) which is converted to the mammalian lignans enterodiol and enterolactone (EL) by ruminal microbiota. Feeding FM to dairy cows increases linearly EL concentration in milk but enterodiol is not detected. The objectives of the study were to determine the length of time to obtain peak EL concentration in the milk of dairy cows fed 20% FM and the length of time to return to EL baseline level in milk when cows are switched from high to low intake of flax SDG. A total of 12 multiparous lactating Holstein cows were assigned randomly to one of two feeding regimens: the control (CO) diet was fed for 6 weeks or the FM diet was fed from week 0 to 3 inclusive and then cows were switched to the control diet from week 3 to 6 inclusive. Milk samples were taken weekly for EL analysis. There was a significant interaction between feeding regimen and week for milk concentration of EL as a result of higher concentration of EL from week 1 to 3 for cows on the FM regimen compared with those on the CO regimen. Concentrations of milk EL on the FM regimen maintained uniform high levels from week 1 to 3 and they decreased significantly from week 3 to 4 when the CO diet was reintroduced in week 3. This study suggests that the conversion of SDG to the mammalian lignan EL and the transfer of EL to the mammary gland are well established after one week of feeding 20% FM in the diet of dairy cows and that milk concentration of EL returns to baseline level after one week of FM deprivation.